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The Hulk

Another Prop Thread with Chart

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The Hulk

ok i'm trying to figure out what prop is best based on new gear ratios etc. so i had a 555hp with a 1.25:1 and a 14.5x16 prop which was great setup and possibly under-pitched but i'll never know now. my new boat is way under pitched with a 450hp with 1.76:1 and a 15x14.25 prop. so im trying to put together a basic sheet to find out what "load" of hp vs torque would a prop give me

so this is by NOO means accurate and i would actually LIKE some input, the biggest issue is that the smaller engines need more rpms to generate their full potential vs the big boy SC engines can create high power at lower RPMS so that WILL have an affect but regardless this might give some people some insight on what to try.

so i'm going off the assumption that there "could" be an equal equation for smaller diameter higher pitch to equal the thrust of a bigger diameter and smaller pitch, or throw RPM and gearbox ratios in on that mix there "should" in theory be something that all works out. smaller diameter faster thrust vs larger diameter slower thrust. (taking prop slip out of the equation) 

what i came up with a simple calculation

Est Torque = (hp * gearbox ratio)

Prop # = (diameter * pitch)

LOAD = (prop # / Est Torque)

Thrust Power = (thrust mph * prop #)

now look at the lower half where i start playing with the prop pitch and putting in my "current" rpms of my old 23lsv boat and my new 25lsv boat, you can see currently i'm producing less power on my new boat at surf speed which makes me believe i'm NOT loading this beast enough yet.

Secondly with my current prop i'm only about 26% load ratio, if i bump that up until i hit around 33% load ratio that puts me right at a 15x17.75 or the ACME 2401,  Now in theory if i had all my hp at lower rpms that woul dlower me down to around 2700rpms to equal the same thrust power as what i'm needing now. obviously its not a SC engine so it takes higher rpms to get that HP so thats the issue so i'm figuring meet somewhere in the middle. so if my theory is correct the 2401 prop 15x17.75 should put my surf RPMs in the 3200-3400rpm range.

@bbattiste247 is running the 410 with the 2401 15x17.75, so if we put his numbers in there we get a load ratio of 36.90% and he is probably on the edge. if he "kept to this misterious 33% rule he would be in the 15x16.25 prop range which i suspect would be best for him, (if he were not adding bow weight).

so perhaps the 33% load range is good for all around performance wake/board/cruise, and if you want to add some bow weight and are NOT into boarding perhaps you can push up to near 37% load number with your prop pitch to lower RPMs slightly.... the kicker is at what point do you lower rpms and not have enough HP so you have to increase rpms to gain it back? tough question but i think these numbers and the way they play should give some insight. it would be very interesting to generate a larger list of peoples setups and rpms, and whether or not bow weight is required etc.. i think we would see a VERY UNIQUE pattern develop and could generate a spread sheet that would allow anyone to figure out what prop they want based on what they want to do.

picture & excel sheet attached if you want to edit go for it!

one thing that should be changed is changing HP for actual torque, but i didnt spend more than 15 mins on this soo..... 

Ok...now i'm ready to be torn apart....ready....set....go!

prop3.jpg

Malibu prop and gears.xlsx

 

Malibu prop and gears.xlsx

Edited by The Hulk

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The Hulk
13 minutes ago, bamaboy said:

Hulk I think if you spent half as much time pondering other things that you spend thinking about hydrodynamics and prop rotation, you could solve world hunger, cure cancer and eradicate tuberculosis.

or if some of you would just take off work tomorrow and come surf so i have a driver!!! then i wouldnt be boored online pondering... but then again if i dont ponder up my next invention i wont be able to pay the bills.. 

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teamerickson

Acme called. They want you to stay out of their business! :tease1:

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bbattiste247

I am impressed with all the calcs and stuff, but it is way over my head. Just get a couple props and try them out. The 2401 on my 2106 23lsv with the 410 surfs at 3000 rpms with weight in the rear, in the bow and four 200+ adults. When the wedge is at 2 clicks from stow, it puts the rpms at 3200 rpms. So run out and get a few props and check them out; you only have a few weeks, but we can surf well into November. Haha. :) 

Your theory is correct. The 2277 (15X15.25) seemed under pitched, and the 2401 (15x15.75) is a little overkill. A 15x16.25 would probably be a happy medium. I read that OJ made a 15x16.25 for another 23lsv owner and he said it was just right.

Edited by bbattiste247

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The Hulk

@bbattiste247 typo on your pitch above for 2401 pitch. if you are down near 3000-3200 then my numbers are very close. i would suspect i'd be around the same then even with the higher hp 450 because last time i looked at the torque/hp charts there is not much difference in our motors hp until the upper 3k rpm range. 'm soo tempted for the 2401 but slightly nervious since i have a 25lsv and more weight, but then again more hp...i love the idea of the 2401, but want to play around with my wave right now and see if bow ballast makes a big differnce or not and if i'll be runnin it all the time or not. i'll have to do @DarkSide plumbing setup if i plan to run bow weight most of the time. i'll have some plumbing to do this winter as i need to make filling/draining much faster.

based on above numbers a SC engine on a 1.46 could probably hit sub 3k rpms easily! anyone out there with a SC propped/pitched up to their potential yet and tried?

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ahopkinsVTX
7 hours ago, bamaboy said:

Hulk I think if you spent half as much time pondering other things that you spend thinking about hydrodynamics and prop rotation, you could solve world hunger, cure cancer and eradicate tuberculosis.

Or be able to spend time out on his boat and actually enjoy the thing! :lol: 

 

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MadMan

I think your "prop #" would be a closer approximation if it was calculated from the square of the diameter (area of a circle varies with the square).

Also, you might find this guys calcs interesting:

http://continuouswave.com/whaler/reference/propellerPowerCurve.html

The graph showing "extra power available" is important to a tow or surf boat.  Having a lot of extra power available, at the surf speed rpm, give 2 advantages.   It takes less throttle to surf and the speed control has more horsepower available to control the speed.

 

Edited by MadMan

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bamaboy
9 hours ago, The Hulk said:

or if some of you would just take off work tomorrow and come surf so i have a driver!!! then i wouldnt be boored online pondering... but then again if i dont ponder up my next invention i wont be able to pay the bills.. 

My bad.  8 hours notice on a Thursday?  Cmon now bro!

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The Hulk
2 hours ago, MadMan said:

I think your "prop #" would be a closer approximation if it was calculated from the square of the diameter (area of a circle varies with the square).

Also, you might find this guys calcs interesting:

http://continuouswave.com/whaler/reference/propellerPowerCurve.html

The graph showing "extra power available" is important to a tow or surf boat.  Having a lot of extra power available, at the surf speed rpm, give 2 advantages.   It takes less throttle to surf and the speed control has more horsepower available to control the speed.

 

yes i considered that as a good idea and it should probably be updated to the "area" x pitch to be more accurate. along with hp substituted to torque with all the engines new BS ratings not being true etc.. 

 

thats great article basically confirming the "extra power" from the SC engines allows more reserve power as you said more stable. now that @MadManhas shown me this link it makes a lot of sense, my old boat with the SC engine did not fluctuate as much when i was surfing and would go ove huge rollers from another boat, it seemed to hold rpms very well, the new boat with 450h seems to fluctuate the RPMS a just a little more amount when going over someone else's rollers. i'm hopping to prop up and reduce some possible under-pitched slip and see if that helps but then i'll have "less reserve"  thanks madman for the link very interesting! 

when do we get one of these as an option? http://www.jegs.com/i/Edelbrock/350/46730/10002/-1?CAWELAID=1710932782&CAGPSPN=pla&CAAGID=15769068431&CATCI=pla-207810388871&gclid=Cj0KEQjwo5--BRCS8ceLjv-XppUBEiQAGp15EEMJiorJ0n6RQ3F9YIpQLgcPgOxwWirxEcnJNEzC-L8aAm1v8P8HAQ

 

 

Edited by The Hulk

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carguy79ta

Just buy it and drop it in..:yahoo:

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The Hulk
1 hour ago, carguy79ta said:

Just buy it and drop it in..:yahoo:

is it possible or something a normal gear head could do? just curious. 

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boardjnky4

I'm confused on how you determined Est Torque... Horsepower isn't static across the RPM range. So it's going to widely depend on what RPM you're at.

I basically have this same question with every formula you came up with. You are WAY oversimplifying and making a TON of assumptions that you can't make.

Edited by boardjnky4

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nyryan2001

The only way I could assess your setup as under pitched is if you, at your heaviest ballast weights (plus wedge)... can do a 0-23 launch so fast you are willing to add pitch and add time to a 0-23 launch.

 

Or... You know your increased pitch will slow your launch times... You're ok with that...and your looking for lower RPMs and gas savings.

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teamerickson

Get a new 15.5 diameter ACME. :)

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The Hulk
3 hours ago, boardjnky4 said:

I'm confused on how you determined Est Torque... Horsepower isn't static across the RPM range. So it's going to widely depend on what RPM you're at.

I basically have this same question with every formula you came up with. You are WAY oversimplifying and making a TON of assumptions that you can't make.

I know that's the problem it needs to get way more complex to account for that

40 minutes ago, teamerickson said:

Get a new 15.5 diameter ACME. :)

which model#

43 minutes ago, nyryan2001 said:

The only way I could assess your setup as under pitched is if you, at your heaviest ballast weights (plus wedge)... can do a 0-23 launch so fast you are willing to add pitch and add time to a 0-23 launch.

 

Or... You know your increased pitch will slow your launch times... You're ok with that...and your looking for lower RPMs and gas savings.

why would i ever do 23mph with ballast? =) not sure i can surf that fast !

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teamerickson

Maybe 2877 or 2879. They have about 6 on the website.

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carguy79ta

Simplisticly it could be swapped in but if it is a car motor like that looks to be, it would live a brief life (it would be fun tho).  It is not meant to produce that horsepower for any longer than 5 to 10 seconds or so. Think sacked out running 3/4 throttle surfing.

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nyryan2001

Well then yes, if you have no need to take ballast up to 23mph you can likely add ballast.

 

is 15" the largest diameter you can go and still maintain 1" clearance?

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WakeSS

I guess I'm not sure of the problem you are trying to solve? I know I just have one afternoon of surfing under my belt with the 25 but fully sacked out (900PNP, driver, 2 pass) I was running 5700 RPM at 10.8 with the 2249. I had to throw those two guys in the bow and dropped the RPMs to ~4800? Assuming that RPM on plane and empty is 40 MPH illustrates the massive amount of slip and effect of prop angle. Boats are not like cars where you assume zero tire slip for final ratio and is probably way beyond my means to calculate for. My mechanical sense tells me if I had more pitch I would not have been able to hold 10.8 in that configuration even though on paper it would look like it should drop the RPMs.

Just throwing out ideas here, it's been 20+ years since I've had a physics or hydrodynamics class and really have no experience with anything relating to prop configuration.

I get it. I'm the same way... collect the data, analyze, make the right decision the first time. But this one I think you're going to have to rely more on user experience and testing than anything else. 

Just buy it and let us know how it works :D

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ahopkinsVTX
4 hours ago, WakeSS said:

I guess I'm not sure of the problem you are trying to solve? I know I just have one afternoon of surfing under my belt with the 25 but fully sacked out (900PNP, driver, 2 pass) I was running 5700 RPM at 10.8 with the 2249. I had to throw those two guys in the bow and dropped the RPMs to ~4800? Assuming that RPM on plane and empty is 40 MPH illustrates the massive amount of slip and effect of prop angle. Boats are not like cars where you assume zero tire slip for final ratio and is probably way beyond my means to calculate for. My mechanical sense tells me if I had more pitch I would not have been able to hold 10.8 in that configuration even though on paper it would look like it should drop the RPMs.

Just throwing out ideas here, it's been 20+ years since I've had a physics or hydrodynamics class and really have no experience with anything relating to prop configuration.

I get it. I'm the same way... collect the data, analyze, make the right decision the first time. But this one I think you're going to have to rely more on user experience and testing than anything else. 

Just buy it and let us know how it works :D

Those Rpms sounds high, really high. When I had the 25 for a weekend we ran wayyyyyyyyyy more weight then that and it didn't ever get above 4300. @The Hulk will have to remind me what prop was on there but I believe the 2249 as well. 

What elevation are you at?

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The Hulk

15 ppl in mine with under pitched 2249 and 750 PNP and wedge and all stock i was about 4200 max still even when lighter im still 4100-4200 dependong on wedge and if someone is in bow. 

10 hours ago, nyryan2001 said:

Well then yes, if you have no need to take ballast up to 23mph you can likely add ballast.

 

is 15" the largest diameter you can go and still maintain 1" clearance?

ill check today to see if a 15.5" will work

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racer808
Just now, The Hulk said:

15 ppl in mine with under pitched 2249 and 750 PNP and wedge and all stock i was about 4200 max still even when lighter im still 4100-4200 dependong on wedge and if someone is in bow. 

ill check today to see if a 15.5" will work

You could give the acme 2937 15x11 or 2951 15x10.5 w/ .105 cupping.  I am pushing 5400 pounds w/ 6.0L 400hp @ 3550 rpm's.  Not sure the tranny  though gearing & stuff

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MadMan
22 hours ago, The Hulk said:

This is more along the lines of what I would want, a lot of cubes (572), so it makes a lot of power without having to buzz the engine or resort to forced induction.  Makes 650 ft./lbs. of torque at 4,500 rpm.

https://www.summitracing.com/parts/nal-19201333/overview/

 

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WakeSS
4 hours ago, ahopkinsTXi said:

Those Rpms sounds high, really high. When I had the 25 for a weekend we ran wayyyyyyyyyy more weight then that and it didn't ever get above 4300. @The Hulk will have to remind me what prop was on there but I believe the 2249 as well. 

What elevation are you at?

Agreed. That was the first pull on this boat and I was like heck no, not buying this if surfing RPM is that high. But it was all due to the prop angle. Every LB I put in the bow or LB out of the rear lowered the RPM. When I was down to maybe 600 per PNP with no bow bag it was back to ~3600.

That was the point I was trying to make in my rambling 4 am post ;)

Forgot elevation - 1000ft.

Edited by WakeSS

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